This invention relates to thin film battery construction, and more particularly to a method of producing thin film batteries having a protective packaging.
The metal lithium of thin film batteries reacts rapidly upon exposure to atmospheric elements such as oxygen, nitrogen, carbon dioxide and water vapor. Thus, the lithium anode of a thin film battery will react in an undesirable manner upon exposure to such elements if the anode is not suitably protected. Other components of a thin film battery, such as a lithium electrolyte and cathode films, also require protection from exposure to air although these components are commonly not as reactive as thin metal anode films. It should therefore be desirable to incorporate within a lithium battery, which includes an anode of lithium and other air-reactive components, a packaging system that satisfactorily protects the battery components from exposure to air.
In the past packaging systems for batteries have been devised which included a shield which overlays the active components of the battery. These shields have been made of a ceramic material, a metallic material, and a combination of ceramic and metallic material. The construction of thin film batteries however has proven to be quite difficult to produce and in providing an appropriate barrier as gas pockets may be captured between the anode and the protective layer during construction.
Another thin film battery packaging system has been devised wherein alternating layers of parylene and titanium are laid over the active components. The alternating layers are provided to restrict the continuation of pin holes formed in the layers during construction. This method of producing a protective layer has been difficult to achieve and has provided a protective layer which remains effective for only a few months.
Accordingly, it is seen that a need remains for a method of producing a protective packaging of a thin film battery which protects the active components from atmospheric elements. It is to the provision of such therefore that the present invention is primarily directed.
In a preferred form of the invention a method of sealing a battery cell comprising the steps of positioning a quantity of epoxy upon the battery cell, and positioning a layer of air impermeably material upon the quantity of epoxy so as to cause the epoxy layer to spread across the battery cell and thereby force gases to be expelled from between the battery cell and the overlying glass layer.